The effects of directional and postural constraints on preferred speed quadrupedal gait patterns were studied by comparing responses to four hand-foot crawling tasks: forward and backward prone (FP and BP) and forward and backward supine (FS and BS). A central question was whether the task dynamics evident at the end-effector level also appear at the joint effector system level. Timing of reversals in each limb's proximal effector system joints was shown to be related to the functional role (propulsion or reaching) of the limb. Within joints, task constraint changes strongly tended to affect reversal times, and time-reversed directional comparisons tended to show “mirroring” responses. Peak reaching positions were also closely associated with forelimb touchdowns and interlimb coordination. Discussion centers on task function, task dynamics, and their influence on effector system behavior.
Larry Forrester and Jill Whitall are with the Department of Physical Therapy, 100 Penn St., University of Maryland, Baltimore, MD 21201.